General anesthesia is often required for mentally retarded children undergoing extensive dental treatment. We experienced a case of dental treatment under general anesthesia in a 14-year-old boy with mental retardation. He was treated on an outpatient basis. He was diagnosed of Noonan syndrome and received heart surgery when he was six years old. Induction using thiopental and vecuronium was uneventful and nasotracheal intubation were carried out. General anesthesia was maintained with sevoflurane for 2.5 hours. After monitoring the patient for 2 hours and confirming his recovery, he was discharged from the day care unit. In summary, we report this successful anesthetic management of a mentally retarded child during dental treatment in as an out-patient.